Lignin is a complex polymer composed mainly of C.sub.6 -C.sub.3 units derived from coniferyl and sinapyl alcohols. Lignin can be regarded as nature's version of the reinforcing steel used in modern building construction, as it provides the strength needed to support the vertical growth of plants and trees.
In order to impart improved strength to plants, it may be desirable to be able to enhance the lignification levels of plants, thereby providing plants more able to resist certain external forces (such as high winds, heavy rains, etc.).
In other situations, where plant strength is not a particular concern, it may be desirable to reduce the lignification levels of a plant to improve the digestability thereof (e.g., with forage crops), to improve the ease of handling (e.g., with cereal crops), and the like.
The production of lignin by plants is a complex process, believed to involve the oxidative dimeization (or polymerization) of phenylpropanoid compounds. The phenylpropanoid route to lignins involves the conversion of shikimic acid to phenylalanine (or tyrosine), which is in turn converted to cinnanic acid (or p-coumaric acid), which is believed to be a precursor to lignin. As noted above, in different situations, it would be desirable to be able to enhance the lignin-forming process, or depress the lignin forming process.